Research on spatiotemporal dynamic speckle suppression mechanism in microstructured waveguide illumination DIC imaging

Abstract

Laser-illuminated imaging, capable of over-the-horizon detection, is extensively utilized in remote sensing and mapping of space, polar regions, and oceans. Under partly coherent laser illumination, random bright and dark patches caused by phase change of light waves due to minute optical path difference in differential interferometric contrast imaging, hence diminishing image quality. This paper investigated the phase-modulated speckle suppression mechanism under partially coherent light and proposed a spatio-temporal dynamic speckle autocorrelation suppression method using microstructured waveguides. By enhancing the conventional reflective differential interference contrast imaging systems with a partially coherent laser as the illumination source and incorporating a point-array microstructure device, spatio-temporal dynamic experiments were conducted through the integration of beam angle and displacement transformations. The results demonstrated that Ir-coated, curved surface-like dot-array homogenizing devices which assisted in imaging effectively achieve spot homogenization and uniform energy distribution, leveraging the scattering suppression capabilities inherent in their material and structural design. In both air and underwater environments, when the light source was uniformly translating or rotating and reached the autocorrelation threshold, the scattering optical range difference was most uniformly distributed; at the same time, when the angle of incidence reached the autocorrelation threshold, the coherence width of the light field was largest, the phase difference was smallest, and the imaging quality was best. Especially in the underwater imaging experiments, the proposed microstructure design combined with the dynamic modulation of the light source demonstrated superior scattering suppression capability, providing an effective way to improve underwater imaging quality.